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Old 08-18-2009, 09:54 PM   #1
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Using 4" PVC for dryer vent


This is not the first home that I have seen this done, but it is the first one that I have been asked by a customer on how to hook up the dryer vent to this. Builders in this area are using 4" PVC pipe for a dryer vent before they pour the slab for the home. This encases the PVC within the concrete floor. The PVC runs from the laundry room to an outside wall of the slab, and are most likely 8-12 feet long. I've seen homeowners split the flexible duct stuff, slip it onto the 4" PVC and use duct tape to make a seal. I've been to different stores around town and none of them have the solution other than to have a sheet metal shop make a transition piece. Usually the PVC is stubbed out 4-6 inches from the wall which doesn't leave any room to work with either. This also seems to make a long run for any dryer to push the hot air out. Any suggestions? Thanks, David

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Old 08-18-2009, 11:10 PM   #2
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Using 4" PVC for dryer vent


Could maybe use "plumber's tape" to tighten the dryer hose to it.

PVC actually sounds like a decent idea, it's cleaner looking and more solid then dryer hose going all over the place (in some cases).

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Old 08-19-2009, 07:15 AM   #3
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Using 4" PVC for dryer vent


Going back one step:

M1502.5 Duct construction.Exhaust ducts shall be constructed of minimum 0.016-inch-thick (0.4 mm) rigid metal ducts, having smooth interior surfaces with joints running in the direction of air flow. Exhaust ducts shall not be connected with sheet-metal screws or fastening means which extend into the duct.

Note that that there is no exception for "except in slabs"
.

The big problem with running dryer ducts in slabs -be they PVC, metal, or anything else -is that the slab acts as a heat-sink, increasing condensation and causing lint to deposit in the pipe - the problem is worst with longer runs and changes of direction.

However because this "seems like a good idea" (perhaps a better idea than galvanized metal) some AHJs do allow the use of PVC dryer duct in slabs. Thus the run in your slab... about which you can now do nothing except suggest (if you have the nerve) the customer re-route the duct run.

As for connections, we are back to M1502 "having smooth interior surfaces with joints running in the direction of air flow", you can't have a connection which slips over the PVC stub (unless it was somehow constructed to produce a smooth interior transition), the practical way to do this is to construct a connector which forms the male end of the connection. I'm not aware of any such factory made connection, if it do not exist it would have to be shop or field fabricated.

-----------------------------------------------------------------------------------

I would just add that many people don't take dryer ducting anywhere near seriously enough.

There around 15,000 residential dryer related fires in the US every year, and many are related to ducting issues.

I'm constantly reporting deficiencies in such ducting, and after disconnection the most common defect is the use of incorrect materials, most often the flexible plastic exhaust ducting sold in every big box home improvement store despite the fact that every instance of its installation violates code (flexible "transition ducts" - the only non-rigid material allowed - must to be listed and labeled per UL 2158).

I know some people are following along behind me and telling homeowners "No problem. It's used all the time. If wasn't okay to use it they wouldn't sell it".

However I've picked least one a additional recent convert to my view - a real estate agent who lit off the dryer at a pre-closing inspection!

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Last edited by Michael Thomas; 08-20-2009 at 10:27 AM.
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Old 08-20-2009, 09:47 AM   #4
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Using 4" PVC for dryer vent


Thanks for the excellent info Michael. I had mentioned to the homeowner that I had thoughts as to the lint build-up within the PVC pipe as it ran under/through the slab. Specifically, how would a homeowner clean it out if needed. I found a rectangular sheet metal dryer vent hook-up at a local appliance store that I can modify slightly to solve this problem. One of the round stubbed out ends fits the dryer perfectly, as it should. The other stubbed out end will have to removed and a new one made to fit the 4" PVC's interior, then some "high quality" duct tape on each end. At least it will be better than the old crimped hose. Thanks, David
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Old 08-20-2009, 10:42 AM   #5
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Using 4" PVC for dryer vent


Quote:
Originally Posted by Thurman View Post
Specifically, how would a homeowner clean it out if needed.
There is a tool to do this, a dryer vent brush, here's an example fo a self-storing version that attaches to a cordless drill:



- http://www.ductsmart.com/6500%20Dryer%20vent%20brush%20tool%2011pcs.htm

a lint brush to clean the filter at the dryer is also handy (there is one included in the kit above, or you can buy them separately):



- http://www.luxuryhousingtrends.com/a...yer-brush-mak/

IMO is is a useful service for a handyman to offer customers, and its also a good reason to get back in touch with your customers yearly.
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Old 08-20-2009, 01:49 PM   #6
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Using 4" PVC for dryer vent


Don't use duct tape on a dryer duct, as it will dry and be brittle soon. Foil tape is a much better choice or in your case - a hose clamp? Connectors not concealed in construction...1501.1 2437.5 is another one that comes to mind.
Be safe, G
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Old 06-15-2010, 03:27 PM   #7
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Using 4" PVC for dryer vent


Quote:
Originally Posted by Michael Thomas View Post
Going back one step:

The big problem with running dryer ducts in slabs -be they PVC, metal, or anything else -is that the slab acts as a heat-sink, increasing condensation and causing lint to deposit in the pipe - the problem is worst with longer runs and changes of direction.


I know this is an older post, but I am curious. the Thermal conductivity of PVC is 0.19 that is at least 100 times less then steel, and in the same range as wood...

How much can the slab act as an heat sink on the PVC... The building code you quoted is for steel exhaust, not PVC... I also wonder how running steel in a slab would affect oxidation/rusting...

For my part, I am looking at making most of the indoor exhaust of my dryer PVC because of it's thermal insulating properties... Running a dryer in the summer will have heat radiate off the steal exhaust, but with PVC you will get much less (if any). and if you dryer's indoor portion of the exhaust is long, this can make a big difference I would think. Also in winter, in cold air that rush in from outside, will radiate off steel as opposed to PVC. Not to mention the PVC is usually very well sealed as opposed to steel...

If I am wrong on any of this, please let me know.

Last edited by rman1968; 06-15-2010 at 03:34 PM.
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Old 06-15-2010, 08:16 PM   #8
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Using 4" PVC for dryer vent


Or do it my way when you knock the pair of scissors down the chute for the lint trap on the dryer, and have to take it all apart. Thought that I had it pretty clean, until I saw the fan for the blower inside the duct inside the dryer. Still have the scar on my Pinky knuckle where I cut it really good while vacuuming the damn thing while apart.
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Old 06-15-2010, 09:36 PM   #9
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Using 4" PVC for dryer vent


""For my part, I am looking at making most of the indoor exhaust of my dryer PVC because of it's thermal insulating properties... Running a dryer in the summer will have heat radiate off the steal exhaust, but with PVC you will get much less (if any). and if you dryer's indoor portion of the exhaust is long, this can make a big difference I would think. Also in winter, in cold air that rush in from outside, will radiate off steel as opposed to PVC. Not to mention the PVC is usually very well sealed as opposed to steel..." --------- has to be steel---

"The following building code requirements are the current minimum code standards, as taken from the IRC Code & Commentary 2006, required for crawlspaces in One and Two family dwellings, and based on Kentucky Amendments to the 2007 Kentucky Residential Cod 1.Domestic Clothes Dryer Ducts. (IMC 504.6) “Exhaust ducts for domestic clothes dryers shall be constructed of metal and shall have a smooth interior finish. The exhaust duct shall be a minimal nominal size of 4 inches in diameter.
  • Clothes dryer transition ducts used to connect the appliance to the exhaust duct system shall be limited to single lengths not to exceed 8 feet and shall be listed and labeled for the application. Transition ducts shall not be concealed within construction.” [Note: Once they pass through a wall, floor or ceiling the code determines the duct is concealed and must be an “exhaust duct” and not a “transition duct”.]
  • “Within the context of this section, a transition duct is a flexible connector used as a transition between the dryer outlet and the connection point to the exhaust duct system. Transition duct connectors must be listed and labeled as transition ducts for clothes dryer applications. Transition ducts are currently listed to comply with UL 2158A… Transition ducts are metalized (foil) fabric supported on a spiral wire frame. They are more fire resistant than the typical plastic spiral duct. Transition duct connectors are limited to 8 feet in length and must be installed in compliance with their listing and the manufacturer’s instructions. “These duct connectors must not be concealed by any portion of the structure’s permanent finish materials such as drywall, plaster paneling, [e.g. flooring, ceiling, wall], built-in furniture or cabinets or any other similar permanently affixed building component; they must remain entirely within the room in which the appliance is installed (Section G2439.5, International Fuel Gas Code, Chapter 24, 2006 IRC).” Transition duct connectors cannot be joined to extend beyond the 8-foot From: http://www.hcpdc.com/pdf/Dryer%20Ven...quirements.pdf
Be safe, Gary
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Old 06-30-2010, 10:44 PM   #10
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Using 4" PVC for dryer vent


I'm just a common sense DIY'er, but I haven't burned the house down yet. I do make sure my homeowners is paid on time or early.

My dryer vent is 22' with one 90deg turn (within factory specs, but not sure about local code. I used 2 10' sections of 4" PVC with metal exiting the dryer and the house. I used foil tape (real duct tape) on the inside of the pipe at each connection to ensure smooth transitions. Since this runs through the joist between floors, I filled the empty space with fiberglass insulation. The pipe is sloped to drain condensation to the outside. The rigitity of the PVC allows for periodic cleanout.

no problems for ten years so far.

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